The present invention relates generally to clutch assemblies and more particularly to a clutch assembly of the overrunning type whereby when a maximum level of torque transmission through the clutch is achieved, the clutch will automatically disengage thereby to limit the torque transmission therethrough.
More specifically, the invention relates to the type of clutch assembly wherein a driving member and a driven member are arranged with a shift ring interposed therebetween with axial movement of the shift ring operating to effect engagement and disengagement of the driving and driven members. Generally, the shift ring may be positively engaged and disengaged with the driven member by devices which effect engagement and disengagement by axial movement of the shift ring. However, engagement of the shift ring with the driving member is generally determined by the amount of torque transmission which is established. When the upper level of torque transmission has been achieved, the driving member may disengage from the shift ring thereby causing, by appropriate mechanisms, axial movement of the shift ring to also disengage the shift ring from the driven member.
On one known prior art assembly of this type, for example a torque limiting clutch with freewheeling action known from German DT-AS No. 2,540,489, there is provided a torque limiting clutch consisting of a driving and a driven clutch member between which a shift ring is arranged for torque transmission. The shift ring is axially moveable and is provided with sectional or castellated-type driving members which effect interengagement between the shift ring and one of the clutch members. When a predetermined torque is exceeded, the shift ring disengages. In the case of this known embodiment, the shifting action of the shift ring is effected as a result of spring-loaded shift pins.
A disadvantage of known embodiments of this type is that there is provided a spring which is arranged between one clutch member and the shift ring which rests against both parts during the freewheeling action of the clutch assembly by creating a frictional force. This results in undesired heat generation in the clutch as well as creating the danger that the clutch may shift again into the driving mode because of the residual frictional forces which are developed.
Because of the use of spring-loaded shift pins in such known torque limiting clutches, and because the springs which are provided tend to create forces acting against other springs which are arranged between the shift ring and one of the clutch members, it becomes necessary that the springs be designed with certain spring characteristics so that the forces which are developed may be balanced. Obviously, this can be a very difficult requirement to fulfill particularly where mass production techniques must be utilized.
Further considerations which arise during the operation of prior art torque limiting clutch assemblies relate to the fact that after the clutch disengages as a result of reaching a predetermined level of torque transmission, the clutch must be reengaged manually into the driving position. For this purpose, the shift ring is provided with shift bores at its outer circumference. In the operation of such prior art devices, a pin may be inserted into the shift bores and the clutch may be reengaged by turning the shift ring against the sense of rotation. However, this operation tends to become tedious and gives rise to disadvantages since, for example, in the case of a tractor vehicle, the driver must leave his seat or the reengagement operation of the clutch must be performed by a second operator.
Thus, it will be found that in clutch assemblies of the prior art several disadvantages of the type discussed above will arise and it is, accordingly, the aim of the present invention to overcome problems of this nature.